By 2100, Deadly Heat May Threaten Majority of Humankind

Up to 75 percent of people could face deadly heatwaves by 2100 unless carbon emissions plummet, a new study warns.

4 Minute Read

By Stephen Leahy

PUBLISHED June 19, 2017

A new study has found that 30 percent of the world’s population is currently exposed to potentially deadly heat for 20 days per year or more—and like a growing forest fire, climate change is spreading this extreme heat.

“Lethal heatwaves are very common. I don’t know why we as a society are not more concerned about the dangers,” says Camilo Mora of the University of Hawaii at Manoa, the study’s lead author. “The 2003 European heatwave killed approximately 70,000 people—that’s more than 20 times the number of people who died in the September 11 attacks.”

Dangerous heatwaves are far more common than anyone realized, killing people in more than 60 different parts of the world every year. Notable deadly heatwaves include the 2010 Moscow event that killed at least 10,000 people and the 1995 Chicago heatwave, where 700 people died of heat-related causes.

Heatwaves have also claimed victims more recently. In the last two weeks, dozens have died in India and Pakistan’s current heatwave, with temperatures spiking to a record 128 degrees Fahrenheit (53.5 degrees Celsius). And there have been heat-related deaths already in the U.S. this summer.

Counting Victims

Mora and an international group of researchers and students examined more than 30,000 relevant publications to find data on 1,949 case studies of cities or regions where human deaths were associated with high temperatures. Lethal heatwaves have been documented in New York City, Washington, D.C., Los Angeles, Chicago, Toronto, London, Beijing, Tokyo, Sydney, and São Paulo.

Those facing the greatest risk live in the wet tropics, where only slight increases in average temperatures or humidity can result in deaths. However, heat can be deadly even at moderate temperatures of less than 86 degrees Fahrenheit (30 degrees Celsius) if it’s combined with very high humidity, Mora ays.

The human body’s internal temperature likes to be between 98.6 to 100.4 degrees Fahrenheit (37 to 38 degrees Celsius); any warmer, and it’s a fever. As temperatures rise, the body reacts by sweating to try and cool down.

In this photograph from August 9, 2010, people rest on the Manezhaya Square just outside the Kremlin in Moscow, Russia. In 2010, the Russian capital became engulfed by poisonous smog from wildfires and a sweltering heat wave that killed some 55,000 people across western Russia.

Photograph by Ivan Sekretarev, Assoiated Press

The young and elderly, who disproportionately lack resources and are more socially isolated, are left the most vulnerable. The overwhelming majority of 15,000 heat-related deaths in France during the 2003 European heatwave were 75 or older, many of whom were living on their own, said Keller.

Thousands of people have died in India from the heatwaves in recent years. Another new study published in Science Advances found that the number of heatwaves in India killing more than 100 people increased 2.5 times between 1960 and 2009—an uptick likely due to climate change, says study co-author and University of California, Irvine professor Steven Davis.

Yet India’s mean temperature has only increased 0.9 degrees Fahrenheit (0.5 degrees Celsius) in the past 50 years, a mild increase in comparison to other parts of the world.

Small increases in mean temperatures can have a major impact in tropical countries, especially amongst the poor who are extremely vulnerable, Davis notes.

Global Warming 101Global warming could do more than just melt polar ice. It could change our maps, and displace people from cities and tropical islands.

“In Chicago people can escape the heat, but that’s not the case for many poor people in India,” he says.

Temperature measurements reveal that summers in 92 percent of U.S. cities have become hotter since 1970. Cities in Texas and the Intermountain West are the most affected, according to data compiled by ClimateCentral. It shows summers in Milwaukee are now 2.4 degrees Fahrenheit (1.34 degrees Celsius) hotter on average, 3.3 degrees Fahrenheit (1.6 degrees Celsius) hotter in Dallas, and 3.8 degrees Fahrenheit (2.1 degrees Celsius) in Salt Lake City.

“This is what climate change means on the ground,” says Davis. Nor is it surprising there are 60 killer heatwaves a year, he added. Hotter temperatures are driving people to leave their homes and migrate. (Meet America's first official climate refugees.)

“Our attitude towards the environment has been so reckless that we are running out of good choices for the future,” says Mora of the University of Hawaii.

“For heatwaves, our options are now between bad or terrible,” he adds. “Many people around the world are already paying the ultimate price of heatwaves.”